A population of transition disks around evolved stars: Fingerprints of planets? Catalog of disks surrounding Galactic post-AGB binaries

TL;DR

This study catalogs disks around post-AGB binary stars, identifies transition disks linked to planetary activity, and suggests giant planets influence disk evolution and stellar surface composition, offering insights into late-stage star and planet formation.

Contribution

It provides the first comprehensive catalog of post-AGB binary disks, identifies transition disks, and proposes a planetary mechanism for their formation and evolution.

Findings

8-12% of systems have transition disks.

Transition disks are linked to refractory element depletion.

Giant planets may carve holes in disks, affecting star evolution.

Abstract

Post-asymptotic giant branch (post-AGB) binaries are surrounded by massive disks of gas and dust that are similar to protoplanetary disks around young stars. We assembled a catalog of all known Galactic post-AGB binaries with disks. We explore the correlations between the different observables with the aim of learning more about potential disk-binary interactions. We compiled spectral energy distributions of 85 Galactic post-AGB binary systems. We built a color-color diagram to differentiate between the different disk morphologies traced by the infrared excess. We categorized the different disk types and searched for correlations with other observational characteristics of these systems. Between 8 and 12% of our targets are surrounded by transition disks, that is, disks having no or low near-infrared excess. We find a strong link between these transition disks and the depletion of refractory elements on the surface of the post-AGB star. We interpret this link as evidence of a mechanism that stimulates the dust and gas separation within the disk and that also produces the transition disk structure. We propose that such a mechanism is likely to be due to a giant planet carving a hole in the disk, effectively trapping the dust in the outer disk parts. We propose disk evolutionary scenarios, depending on the presence of such a giant planet in the disk. We advocate that giant planets can successfully explain the link between the transition disks and the observed depletion of refractory materials. If the planetary scenario is confirmed, disks around post-AGB binaries could be a unique laboratory for testing planet-disk interactions and their influence on the late evolution of binary stars. The question of whether such planets are first- or second-generation bodies remains to be considered. We argue that these disks are ideal for studying planet formation in unprecedented parameter space.